Studies on the structure of avian retroviruses will be continued. This will include (1) completion of current studies of topography of the proteins using reversible chemical crosslinkers in conjunction with radioimmune precipitation and two-dimensional gel electrophoresis; (2) tryptic and serological analysis of envelope protein; and (3) synthesis and processing of viral protein in cell-free extracts. Related studies, on the cell-free synthesis and processing of viral proteins, will be carried out with the two RNAs (MW 10 to the 6th power; 0.5 times 10 to the 6th power) of Black Beetle virus (BBV). This virus, by contrast with retroviruses is nonenveloped and contains but a single coat protein which is processed during virion assembly. We will study the synthesis and processing of this protein in cell-free extracts and in infected Drosophila cells grown in culture. BBV RNAs, which are very active in the cell-free system, will be useful tools for studying and improving the activity of the cell-free protein-synthesizing system. Further studies on BBV assembly may produce insights into the mechanism which insures that each virion acquires a correct pair of RNA molecules.